QuakeIndex

Earthquake · reviewed by a seismologist

M 3.8mw

Earthquake near Rio Dell, CA

No earthquake was likely felt in Rio Dell in the 24 hours to 1:34 am PST (09:34 UTC). The last one was M 5.0, 126 km (78 mi) W, at 8:56 pm PST on 4 November 2026, estimated intensity II (weak) in town; 145 felt reports to USGS. Every earthquake near Rio Dell

This page: a magnitude 3.8 earthquake was recorded 10 km (6 mi) west-southwest of Rio Dell, CA, at 8:18 am PDT on 4 April 2022 (15:18 UTC), 21 km deep. 60 people have reported feeling it to USGS.

USGS: 10km WSW of Rio Dell, CA

8:18 am PDT, Apr 4, 2022 · · 21 km deep · released about 7.6 tons of TNT

Every earthquake near Rio Dell Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Humboldt County 35 kmTrinity County 95 km
Distance rings around the epicentre, with the nearest towns at their true direction and later quakes as coloured dots. Not a shaking map — see the USGS ShakeMap for that.
When
8:18 am PDT on 4 April 2022 ()
Where
10 km (6 mi) west-southwest of Rio Dell, CA · earthquakes near Rio Dell
Magnitude
M 3.8 (mw)
Depth
21 km below the surface
Felt
60 reports · strongest reported intensity III
Measured shaking
intensity III (ShakeMap)
Nearest
Humboldt County, 35 km NE
Nearest mapped fault
Little Salmon fault, 15 km from its surface trace — near is not the same as on
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 1187 days ago

This was a small earthquake. Shaking like this is often felt indoors nearby and very rarely causes damage.

At this magnitude and depth, people at rest would likely notice it out to about 80 km (50 mi) from the epicentre. In Rio Dell, 10 km away, the estimate is intensity III (weak). Estimated from magnitude, depth and distance with the intensity equation USGS Did You Feel It? uses; felt reports, where there are any, are the measurement.

Likely felt in: Rio Dell 10 km, intensity III · Ferndale 11 km, intensity III · Fortuna 14 km, intensity III · Humboldt Hill 27 km, intensity III · Eureka 36 km, intensity II · Bayside 42 km, intensity II. Estimated for each town centre; each link is that town's own record.

How big was it?

This earthquake released about 7.6 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 4.8 would have released about 32 times as much.

  1. Northridge, California 1994 M 6.7 22,000× the energy of this one
  2. Mineral, Virginia 2011 M 5.8 1,000× the energy of this one
  3. Magna, Utah 2020 M 5.7 710× the energy of this one
  4. This earthquake M 3.8 about 7.6 tons of TNT
  5. Around the size people start to feel M 3.0 this one released 16× more

Energy from the Gutenberg–Richter relation (log10E = 1.5M + 4.8), rounded to two figures; bar length is magnitude, which is already a logarithm of energy. Magnitudes of past earthquakes from the USGS catalogue.

For this area

The largest earthquake within 50 km since 2016 was M 6.2 on 2021-12-20 — about 4,000 times the energy of this one.

Before 2016, the USGS record lists 37 earthquakes of M5 or more within 50 km; the five largest:

  1. 7.2 The 1992 Petrolia, California Earthquake · 16 km S of this epicentre
  2. 6.6 32 km SW of Ferndale, California · 31 km WSW of this epicentre
  3. 6.5 The 1932 Eureka, California Earthquake · 28 km NNW of this epicentre
  4. 6.5 30 km WSW of Ferndale, California · 30 km W of this epicentre
  5. 6.5 The 2010 Eureka, California Earthquake · 44 km WNW of this epicentre

Since 2016: the QuakeIndex catalogue (US, M1.5+), built from the USGS FDSN event service. Before 2016: USGS ComCat, M5+ from 1900. Distances are between epicentres. This is the record, not a forecast.

Where

Epicentre 40.4817, -124.2187. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Humboldt County, CA 35 km (22 mi) NE earthquakes near Humboldt County
Trinity County, CA 95 km (59 mi) ENE earthquakes near Trinity County
Mendocino County, CA 134 km (83 mi) SSE earthquakes near Mendocino County

Places and coordinates from the US Census Bureau Gazetteer (2024). Distances are from the epicentre.

Aftershocks so far

56 earthquakes have been recorded within 50 km since this one.

  1. 1.6 11km SSW of Ferndale, CA
  2. 1.7 12km SSW of Ferndale, CA
  3. 2.0 19km SE of Petrolia, CA
  4. 2.0 19km SE of Petrolia, CA
  5. 2.2 2km ESE of Hydesville, CA
  6. 2.1 8km S of Ferndale, CA
  7. 1.7 10km SSW of Ferndale, CA
  8. 1.8 12km SSW of Ferndale, CA
  9. 2.5 14km WSW of Petrolia, CA
  10. 2.6 33km W of Petrolia, CA
  11. 2.6 6km NNW of Petrolia, CA
  12. 2.0 22km W of Petrolia, CA
  13. 2.3 11km SSW of Ferndale, CA
  14. 2.2 4km W of Humboldt Hill, CA
  15. 1.6 10km SSW of Ferndale, CA

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of . QuakeIndex does not forecast aftershocks. When USGS issues an operational aftershock forecast it appears on the USGS event page.

On USGS

QuakeIndex does not issue warnings. For earthquake early warning see ShakeAlert.